The present invention relates to dislocatable prestressed rolling bearings and, particularly to use thereof for mounting land-going motor vehicle steering columns.
The invention relates to rolling bearings intended to provide the connection between a shaft and a support so that, besides a degree of freedom in relative rotation between shaft and support being possible, a certain degree of freedom in relative axial translation between shaft and support might also be possible under certain completely exceptional circumstances. The invention also relates to the application of such a rolling bearing to the steering columns particularly of land-going motor vehicles.
In numerous industrial fields, it is necessary to be able to mount a shaft on at least one support so that such shaft and such support can normally turn in relative rotation about their common axis without thereby being able to move translationally along this axis, except for extreme exceptional circumstances.
Such a situation is encountered, for example, in the motor industry, for mounting steering columns of a type which are capable of disconnecting or otherwise deforming, for example by compression or retraction, so that they do not project into the passenger compartment in the event of violent impacts with a significant axial longitudinal component, referenced with respect to the vehicle, so as not to endanger the life of the driver.
As is known, conventionally a steering column is composed of a support, column sheath or tube, which is fixed to the driving position of the vehicle through the use of fittings, gusset plates or the like, connected to the structure or shell. Such a steering column is also composed of an actual shaft, often in several sections which, through use of the steering wheel, transmits steering instructions from the driver to the wheels of the vehicle by the interposition of a steering box and steering gear. The shaft is mounted, at least partially, in the support, sheath or tube, with the aid of rolling bearings, most often roller or needle bearings, so as normally to allow just one degree of freedom of movement in relative rotation about the common axis of the shaft and of the support, sheath or tube, to the exclusion of any other degree of freedom of movement, such as an axial translation, except, for example, in the event of a frontal impact or an impact with a large longitudinal component, referenced with respect to the conventional longitudinal axis of the vehicle, this impact exceeding a determined threshold of the order of 250 daN.
Such a subassembly which effectively participates in passive safety must be reliable, satisfy strict and sometimes apparently contradictory standards, while remaining of modest cost.
Such a steering column must, for example:
be free of any play, without the slightest pinching or interference that would prevent relative displacement; PA1 allow rotation with a torque which does not exceed 0.06 Nm, for example; PA1 have wear durability which conventionally corresponds at least to the average anticipated life of the vehicle; PA1 resist radial compressive stresses which may arise during attempts at a break-in when the steering lock is engaged, under the action of a torque of 250 Nm; PA1 be strong, by virtue of its rigidity, with a displacement which does not exceed 0.2 mm under a load of 2.5 daN transmitted by the steering wheel; PA1 under normal operation, resist any longitudinal translation of the shaft with respect to the support, by sliding; PA1 and, however, give longitudinally and or disconnect under axial loads exceeding a prefixed limit so as to contribute to the safety of the driver so that the latter is not injured or bruised following violent contact with the steering wheel on the occasion of a hard impact or collision.
This brief, non-exhaustive, list illustrates how difficult it is to satisfy all these technical specifications taking into account the economic requirements which have to be faced.
A solution usually utilized for solving this type of difficulty consists in making use of very particular ball- or roller- or needle-rolling bearings which are very different from rolling bearings with a circular, conical or spherical raceway. In fact, the rolling bearings used for this type of application have, for example, polygonal, often triangular, raceways or races. These bearings make it possible to compensate for the variations in dimensions resulting from manufacturing tolerances between support, tube or sheath and shaft while ensuring the total absence of play.
Solutions are, for example, illustrated by FR 2,193,443 and FR 2,586,069 to which reference may usefully be made. These solutions are not, however, totally satisfactory, because they require relatively numerous constituent parts and relatively complex multiple mounting operations, and all adversely impacting costs.